The present invention relates generally to the interior design of a diesel engine in the area of the cylinder head and cylinder liner. More particularly the present invention pertains to the modified configuration of a cylinder liner and the design of a spring-energized combustion seal which is assembled within the cylinder liner and used to maintain the seal between the cylinder liner and the cylinder head so as to prevent leakage of cylinder combustion gases.
One of the needs in designing an internal combustion engine, such as diesel engine, is to seal the interface around the cylinder bore between the cylinder liner and cylinder head. Currently one means of providing a sealed interface is to use a gasket and fire ring. However, when subjected to the high combustion temperatures and pressures in the cylinder, as experienced by present engines, the gasket and fire ring combination fails (prematurely) during endurance testing. Such testing indicates that a premature failure will likely result during actual engine operation.
One problem revealed to the present inventors during compression testing of existing designs was the nonuniform loading around the circumference of the standard gasket and fire ring combination. In the lightly loaded areas there was a leakage of combustion gases. Since it may be asked whether the problem of leakage can be solved by increasing the bolt clamp loads on the head, the answer is "no". It has been found that an increase in the bolt clamp loads on the head does not improve the sealing due to the fact that the bolts relax at elevated temperatures. Further, it has been found that increased clamp loads can locally yield (deform) the cylinder head.
In order to address the concern and solve the problems of leakage and premature failure, the present inventors have incorporated into the cylinder liner a spring-energized seal, made of a superalloy metal which is positioned in a counterbored groove (two-sided) which is machined into the upper margin of the corresponding cylinder liner. The designed seal is disposed in contact in an axial or vertical direction with both the cylinder liner and the cylinder head. The spring-energized seal and cylinder liner assembly of the present invention creates a tightly sealed interface around the entire circumference of the cylinder liner. Compression testing with the present invention has shown excellent loading around the entire circumference without leakage and without any premature failures. A suitable spring-energized sealing ring for this application may be available from various manufacturers, including Advanced Products Company of North Haven, Conn. However, manufacturers of such sealing rings have not promoted their use in the manner proposed in the present invention.
With the present invention it is possible to maintain the pressure in the cylinder head without leakage. The corresponding clamp load needed to activate the seal is roughly 30 percent lower than is what is required for a gasket and fire ring combination. Due to the fact that high temperature alloys are used in this area of the engine, the spring-energized seal can be located closer to the cylinder liner bore and function at much higher temperatures. Having the spring-energized seal as close as possible to the liner bore allows the designer to control the clearance volume distribution within the combustion chamber (i.e., reduces the amount of dead volume in the combustion chamber at piston top dead center). Structurally, the use of superalloy materials allows the design to function at elevated temperatures. Such materials exhibit far greater strength at high temperatures in the range of 1500.degree. to 2000.degree. F. than do conventional alloys.
An added benefit of having lower clamp loading requirements is a reduction in cylinder liner distortion which improves piston ring sealing. The spring-energized feature of the present invention helps to maintain positive sealing contact between the seal and the mating components during any operating condition.
In the future, the present inventors expect the trend in diesel engine design to be directed towards smaller, more efficient engines. With a low heat rejection engine the need for water cooling the head is eliminated along with all the supporting hardware. The result of requiring less cooling hardware is a lighter engine and more pay load carrying capacity. The lower activation loads required by the spring-energized seal allow the surrounding hardware to be made smaller. Reduced activation load requirements result in smaller diameter cap screws, the mating flange bearing stresses decrease or the bearing areas can be reduced. In addition, with the spring-energized seal located closer to the liner bore, the spacing between cylinder liners can be reduced in the engine block. This allows the overall engine length to be made smaller.
The inventors are aware of a few earlier patents which pertain generally to cylinder head gaskets, sealing rings and spring seals. These earlier patents include the following:
______________________________________ Patent No. Patentee Issue Date ______________________________________ 3,433,490 Teucher et al. March 18, 1969 3,519,278 Fuhrmann et al. July 7, 1970 4,369,980 Backlin Jan. 25, 1983 4,508,356 Janian Apr. 2, 1985 4,602,888 Court et al. Jul 29, 1986 5,112,066 Remmerfelt May 12, 1992 4,397,472 Czernik Aug. 9, 1983 4,480,844 Kozerski Nov. 6, 1984 4,528,959 Hauser, Jr. July 16, 1985 ______________________________________
While these listed patents pertain generally to the present invention, Teucher et al. does disclose a metal sealing ring including a sheath with a C-shaped cross section and between the arms of the sheath an annular, helically-wound tension spring. In order to compare and contrast the present invention from the Teucher et al. patent disclosure, it is important to recognize and understand that the flat gasket presented by the Teucher et al. disclosure is primarily for sealing combustion gases, lubricant and coolant passageways (5). An important function of sheath (13) is to overlap lug (10) to attach the combustion seal to sheet (11) which seals coolant. In addition, compression of spring (16) is affected by compression of sheet (11).
In contrast, the combustion seal of the present invention does not attach to, or interact with, any other sealing element. The C-shaped outer metal jacket and coiled spring of the present invention are directly exposed to the combustion gases. Without coolant in the cylinder head, the combustion seal of the present invention is exposed to elevated temperatures. Consequently, the components of the present invention are constructed from superalloy materials in order to provide the requisite high strength and corrosion resistance at these elevated temperatures.
The Fuhrmann et al. patent reference is also of interest for its disclosure of a sealing arrangement which includes an annular coil spring surrounded or encased by a sheath. In order to compare and contrast the present invention from Fuhrmann et al., it is important to recognize and understand that while that the Fuhrmann et al. patent disclosure may have some similarity to the present invention it does not disclose nor suggest the unique features which have been developed by the present inventors. Specifically, as is illustrated and described in the Fuhrmann et al. reference, its seal is placed in the block not the cylinder liner and is shielded from the combustion gases. With the Fuhrmann design, the liner/block mating surface inboard of the seal provides some measure of sealing. The seal prevents leakage from occurring across the outboard liner/block mating surfaces. In the present invention the seal is inserted directly into the combustion chamber and the C-shaped configuration opens inwardly towards the center of the cylinder liner (i.e., bore). With the spring-energized seal positioned so it is adjacent to the liner bore, combustion gases are used to activate the seal. The pressure differential across the cross section of the seal forces the top and bottom legs of the sheath outwardly against the top and bottom mating flange surfaces. As is clearly illustrated, referring to either FIG. 1 or FIG. 3 of the Fuhrmann et al. reference, the block radially outwardly of the seal is flush with item 10 which is the cylinder head. Additionally, and more importantly, either the liner (FIG. 1) or the wall of the block which defines the cylinder bore is also flush with item 10 (cylinder head). In the present invention the only block and head portions which are flush to one another are those which are radially outwardly of the combustion seal. Radially inwardly of the combustion seal the cylinder liner is not flush with the cylinder head. It is by this means of construction that the combustion seal of the present invention is exposed to the interior of the combustion cylinder and thus exposed to the combustion gases and directly exposed to the higher temperatures.
The embodiment shown in FIG. 9 involves a coating on the C-shaped sheath: ". . . covering layers 40 and 41 made of an extremely soft material, such as soft rubber . . . ". A notable improvement offered by the present invention is to use a metallic plating of intermediate hardness to withstand the loads and high temperatures at the periphery of a diesel engine combustion chamber.
In view of the function, performance, effectiveness and structural differences and improvements which are provided by the present invention relative to the listed prior patents and in particular Teucher et al. and Fuhrmann et al. the combustion seal assembly of the present invention provides a preferred design.